The present invention relates to a handy pneumatic power saw, and more specifically to an air-tight sealing arrangement for a handy pneumatic power saw which presents an air leakage, and ensures a positive reciprocating motion of the saw blade.
FIGS. 1 and 2 show a handy pneumatic power saw according to the prior art. This structure of handy pneumatic power saw is generally comprised of a casing 10, an actuating unit 11, a saw blade 12, an end block unit 13, and a trigger 14. The casing 10 defines a longitudinal sliding hole 100 and an actuating chamber 101. The longitudinal sliding hole 100 and the actuating chamber 101 have different diameters, and are longitudinally aligned. The actuating unit 11 is mounted in the actuating chamber 101, comprised of a piston rod 110, a piston 111 fixedly mounted on one end namely the rear end of the piston rod 110, an air cylinder 112, two rubber cushions 113 fastened to front and rear sides of the piston 111, a valve 115 fastened to one end namely the rear end of the air cylinder 112, and a gasket 130 retained between the end block unit 13 and the casing 10. An opposite end namely the front end of the piston rod 110 is inserted through the longitudinal sliding hole 100, and connected to the saw blade 12. The saw blade 12 is fastened to the front end of the piston rod 110 by a chuck 114. The end block unit 13 is fastened to the rear open end of the casing 10 by screws. The trigger 14 is pivoted to the end block unit 13. By means of operating the trigger 14, the mechanism of the end block unit 13 which is comprised of spring holder means, bolt means, socket means, push rod means, etc., is driven to close/open the air passage, and therefore the piston rod 110 is moved with the piston 111 to reciprocate the saw blade 12. This structure of the handy pneumatic power saw is not durable in use because the moving parts wear quickly with use. When the moving parts of the handy pneumatic power saw begins to wear, an air leakage may occur, thereby causing the saw blade 12 unable to be smoothly reciprocated. Because the piston rod 110 and the piston 111 are reciprocated to compress and release air pressure, the reciprocating movement of the saw blade 12 becomes unstable when an air leakage occurs. When the actuating unit 11 is installed in the actuating chamber 101, the air cylinder 112 is forced by the valve block 115 against the front side wall of the actuating chamber 101. However, because the air cylinder 112 and the valve block 115 both are made from metal, they are not compressible. When the piston 111 is reciprocated, the front rubber cushion 113 is intermittently forced to strike against the front side wall of the actuating chamber 101, causing a backward force to be produced and transmitted to the end block unit 13. Frequently giving a backward force to the end block unit 13 causes the mounting screws of the end block unit 13 to be loosened and a gap to be produced between the end block unit 13 and the casing 10. When a gap occurs between the end block unit 13 and the casing 10, a leakage of air becomes inevitable.